In all types of surfacing operations for workpieces, it is necessary to establish a desired relative position between the workpiece support or bed and the surfacing means to accomplish the desired result. Often the thickness of the workpiece itself is a factor in establishing this relative position.
In a conventional abrasive belt grinding machine, a machine frame suspends an abrasive grinding head in a fixed position over an adjustable bed that carries a horizontally moving workpiece conveyor. The grinding head of the abrasive belt grinding machine typically includes a lower contact drum around which an endless abrasive belt is driven, or a platen over which an abrasive belt moves. In any case, a rigid or yielding backing is provided for the abrasive belt at the line or region of abrasive engagement, and it is this region which must be taken into consideration when the elevation of the workpiece bed and conveyor is adjusted.
One of the problems unique to abrasive belt grinding machines in position setting of the bed is the thickness of the abrasive belt. Abrasive belts vary rather substantially in thickness from fine to coarse grits, and this thickness must be taken into consideration if accurate results are to be obtained. If belt thickness is ignored, a precision finishing operation can vary significantly beyond accepted tolerances simply because an abrasive belt has been changed.
Further, many abrasive belt grinding machines are used for sequential operations starting with a coarse abrasive belt for material removal and ending with a fine abrasive belt to obtain the desired surface finish. If belt thickness is not taken into consideration throughout these operations, many trial and error adjustments will be necessary with the changing of each belt.
Position setting devices for abrasive belt grinding machines are not themselves novel. However, prior art devices either do not take belt thickness into consideration, or require recalibration each time a new belt is installed. In addition, those devices which are capable of taking belt thickness into consideration are generally sophisticated and expensive.